Talc

Chemical Formula : Mg₃Si₄O₁₀(OH)₂
Hardness : 1
Cleavage : One, perfect
Luster : Pearly on cleavages, otherwise greasy to dull.
Color : Pale green , white, or gray.
Streak : White
Density : 2.82
Diagnostic Features and Trivia : Talc is the definition of hardness of 1 on Moh's scale. The soapy feel of the mineral is due to the hardness of human skin which is around 1.5, and because this is harder than the mineral just touching it, breaks off minute fragments.
Crystal System and Habit : Monoclinic; foliated masses and compact fine-grained aggregates.
Twinning : None
Polymorphs : None
Index of Refraction : plpha=1.538-1.550; beta=1.575-1.594; gamma=1.565-1.600